whats your budget for an upgrade? do you want rebuildables or prebuilt coils?
Mod choices are plenty these days and entirely depends on your budget and type of battery you want in there - lipo, single, dual, triple 18650, 26650, built in batteries, etc. TC with ni200, SS, Ti seems to be standard, so is TCR with the newer mods.
As for tanks. Check out the cerabis ceramic subohm tank by Ceravape. I recommend this due to how easy it is to use and how long their ceramic coils last (advertised as lasting up to 3 months, so far I've gone thru 60mls and the coil is still vaping like new).
With ceramic coils you don't have to prime your coils, just install, fill up, vape.
With ceramic coils you don't have to switch out your coils when changing flavor, just finish vaping the tank and dry burn the coil at a low wattage setting.
With ceramic coils you get great flavor. Its honestly better than the Crown, which is known for flavor. This one is on par with my RTAs and I have alot of RTAs.
The tank is virtually leak free, build quality is top notch, and the AFC/JFC control is just awesome.
Tank is about $26 (angelcigs is where I got mine), coils are $14 for a 4 pack, same price as a cotton wick coil but lasting much much longer.
Only 2 cons I have with this thing.
1. The tank heats up rather quickly, but due to the design of the drip tip, the heat does not transfer to your lips.
2. It guzzles juice and requires at least 40W (I vape the 0.4-0.5ohm coils at around 50W) to vape decently